The invention relates to the field of protective technology, in particular for electrical switchgear assemblies. It relates to an apparatus and to a method for monitoring the operation of a converter in accordance with the preamble to patent claims 1 and 5.
Electrical switchgear assemblies, for example medium, high and low voltage switchgear assemblies, have control and protective devices. Protective devices must reliably detect, identify and locate electrical faults, for example short circuits or line interruptions, and must initiate suitable countermeasures in order to prevent faults from being propagated and system parts from being destroyed. At the same time, however, a protective device should not cause any system parts to be turned off unnecessarily. A protective device must therefore itself also have a high level of reliability. To this end, individual units of the protective device, in particular converters, need to be monitored. Examples of such converters are test amplifiers, digital-to-analog or analog-to-digital converters. A defect in a converter generally results in corruption of measured data and in a faulty response from the protective device.
In a generally known manner, operational monitoring is performed using a redundant design for units in a device: such a unit is of duplicate or triplicate design, and a lack of any match between output signals from the units is used to infer that a unit is malfunctioning. Such redundancy results in the costs of the unit being at least doubled or tripled, however. Another manner of monitoring the operation of an appliance is known from U.S. Pat. No. 4,215,412. In this case, control variables and output variables for an aircraft engine are measured while the engine is operating. A computer-based simulation model of the engine continuously simulates a response of the engine and of the output variables during operation using the measured control variables. To this end, a complex mathematical model with an appropriate level of computational complexity is used. If the continuously changing, calculated and measured output variables do not match, an indicator is activated for an operator. However, producing a simulation model, matching it to a given engine and performing continuous calculations during operation require a high level of complexity.
It is therefore the object of the invention to provide an apparatus and a method for monitoring the operation of a converter of the type mentioned in the introduction which eliminates the aforementioned disadvantages.
This object is achieved by an apparatus and a method for monitoring the operation of a converter having the features of patent claims 1 and 5.
The invention""s method for monitoring the operation of a converter involves detecting whether a value of an input variable for the converter assumes a first prescribed input reference value, and checking whether an output variable from the converter likewise assumes a corresponding, second prescribed output reference value.
This means that the operation of the converter is tested only at occasional instants, specifically only using individual, prescribed values. The fact that only prescribed values are compared with instantaneous values of the input and output variables means that the apparatus according to the invention can be produced using very simple means.
In one preferred variant of the invention, the prescribed values correspond to a value zero for a current, or to a value zero for a voltage, that is to say to a ground potential, and/or to a supply voltage for an electrical system.
The method according to the invention is particularly suitable for monitoring the operation of a converter in a control or protective device for an electrical switchgear assembly. In this context, when a malfunction in the converter is detected, all protective functions which are dependent on this converter are preferably turned off.
Further preferred embodiments can be found in the dependent patent claims.